As this type of sheet cutter are known those which are disclosed in JP-A-6-47696 and JP-A-2005-74598.
In the sheet cutter disclosed in JP-A-6-47696, a movable blade is formed of a thin plate type cutting steel having a cutting blade whose blade edge line is recessed in a V-shape, and a cutout groove is processed at the center portion of the cutting blade. By controlling the reciprocating movement amount of the movable blade, the sheet cutter can perform partial cutting (partial cut) by which a part of a sheet is left at the cutout groove and full cutting (full width cut).
Furthermore, in the case of the cutter disclosed in JP-A-2005-74598, the cutting portion of the movable blade is formed substantially in a V-shape having a pair of slants, and cutouts are formed in the slants forming the cutting portion. The cutouts serve to form cutting residual portions of a sheet. An acicular pointed portion is formed at a portion nearer to the center of the movable blade out of the entrances of the cutouts. The pointed portion sticks into a sheet to smoothly start the cutting operation. This pointed portion is formed by processing the slant surface of the cutting portion over the area from the cutout portion of the slant to the cutout portion at the center (see FIG. 12 of JP-A-2005-74598).
As disclosed in JP-A-6-47696, in the sheet cutter having the cutout groove in the movable blade, a sheet is cut in cooperation of the fixed blade and the movable blade, however, the shearing action on the sheet is lost at the instantaneous time when the fixed blade crosses the cutout groove of the movable blade. At this time, the sheet is pressed against the fixed blade, and torn off and broken at the opening end portion of the cutout groove.
Therefore, there occurs a problem that front and rear sheets are separated from each other in spite of partial cutting or breakage of the sheet progresses to the inside of the sheet when a cutting residual portion is afterwards cut off and thus the sheet cannot be beautifully cut off.
Furthermore, even in the case of the cutter disclosed in JP-A-2005-74598, the acicular pointed portion is formed at a portion nearer to the center of the movable blade out of the entrances of the cutouts, however, an edge having a thickness remains at the entrance of the cutout portion at the side confronting the portion concerned, and thus there is a risk that the same problem as the cutout groove of JP-A-6-47696 may occur.
In addition, the pointed portion disclosed in JP-A-2005-74598 is formed by processing the cutting portion on the slant surface over the area from the cutout portion of the slant to the cutout of the center, and thus a cumbersome polishing work is required for the processing of the slant surface. The sheet cutter has a problem that the edge of the cutting portion is liable to be nicked because the cutting portion is formed on the slant surface and thus the durability of the sheet cutter is lowered.
The present invention has been implemented in view of the situation as described above, and has an object to make manufacturing easy, enhance the durability of a cutting portion and enable excellent formation of a cutting residual portion of a sheet material when the sheet material is partially cut.